Optio s4i

I have just purchased this camera (as a replacement for an S4 which was faulty) and it has problems with autofocus and macro/supermacro modes. The macro modes won't focus at all, and at times the camera refuses to take any picture in these modes. When the focus should be set by half depressing the shutter, this does not work either.

I am going to return it to the dealer, for a replacement, but wondered if this is a problem others have had with this model?